<!DOCTYPE html>  
<html>  
  <head>  
    <title>Data Types</title>  
  </head>
  <body>  
    <script type="text/javascript">  
       var name = "John";
       document.write(name); 
       document.write("<br>"); 
       
       var myNum = 15;
       document.write(myNum); 
       document.write("<br>"); 
   
       var myBool = true;
       document.write(myBool); 
       document.write("<br>"); 
   
       var myUnd;
       document.write(myUnd); 
       document.write("<br>"); 
       
       var myNul = null;
       document.write(myNul); 
       document.write("<br>");
       
       var myNul2 = document.getElementById("aa");
       document.write(myNul2); 
       document.write("<br>");
       
    </script> 
  </body>  
</html>